Separation of solids in a gaseous current



p 1 96 o. R. PRESCOTT SEPARATION OF SOLIDS IN A GASEOUS CURRENT 2Sheets-Sheet 1 Filed March 4, 1965 p 1 1967 D. R. PRESCOTT SEPARATION OFSOLIDS iN A GASEOUS CURRENT Filed March 4, 1965 2 Sheets-Sheet f3 UnitedStates Patent ()fiice 3,341,011 Patented Sept. 12, 1967 3,341,011SEPARATION OF SOLIDS IN A GASEOUS CURRENT Donald R. Prescott, WestNewton, Mass'., assignor to Segredyne Corporation, Cambridge, Mass., acorporation of Massachusetts Filed Mar. 4, 1965, Ser. No. 437,202 11Claims. (Cl. 209-144) ABSTRACT OF THE DISCLOSURE Elongated particleshaving one long dimension are separated from other particles alldimensions of which are less than the long dimension, by moving all theparticles in contact with a gaseous medium, providing a differentialvelocity between the particles and the medium sufficient to align theelongated particles with their longest dimension generally perpendicularto the direction of their flow, thereafter guiding the particles onto aninner surface circular in cross-section, and moving the particlescircularly and downwardly over holes large enough to accept alldimensions of the elongated particles except the long one.

This invention relates to separating mixtures of solid particles. Moreparticularly, it makes possible efiicient separation of elongatedparticles of dimensional integrity and with first dimensions larger thantheir other two from other particles in which no dimension is as largeas said first dimensions.

It is the primary object of the invention to make possible theseparation as just mentioned. A further object is to do so withminimized loss of the elongated particles, even though the particlesfrom which they are separated are thrown out through holes much greaterin diameter than any dimension but the longest of the large elongatedparticles, not permitted to go through the holes. Further objects are toaccomplish this without blocking holes with generally wedge-shaped orother particles, or with fibrous or gummy or other materials; to provideimproved cleaning of the large elongated particles; and to make possiblesaving of desirable materials that would otherwise be Wasted.

Generally speaking, the invention features moving a mixture of theabove-mentioned elongated particles and the abovementioned otherparticles in a stream and in contact with a gaseous medium, giving toall the particles and to the gaseous medium different velocities,directing the stream onto a surface closedly circular in cross-section,and moving the particles therefrom over a perforate member with asurface circular in cross section and interrupted by openings largeenough to accept all dimensions of all said particles except the longestdimension of the said elongated particles. In preferred embodiments, theparticles are pneumatically conveyed, with low weight ratios of gaseousmedium to particles at an initial velocity over 5000 feet per minute;the differential velocity is thereafter provided by increasing thecross-sectional area of a conduit; the particles are guided into athinned stream and tangentially of the closedly circular surface bychanging the direction of the conduit to provide centrifugal forcesbiasing the particles so; and the openings are several times larger thanthe particles to be moved therethrough. In the most preferredembodiment, wood chips (including pegs and matchsticks) are separatedfrom bark, sawdust, grit, and stone in preparation for digestion inpulpmaking for manufacture of paper.

Other objects, features, and advantages will appear from the followingdescription of a preferred embodiment of the invention, taken with theattached drawings thereof, in which:

FIG. ,1 is a broken away view of the inner surface of the perforatemember over which the particles are moving in a downwardly circlingdirection, near the inlet end thereof;

FIG. 2 is a diagrammatic view showing chips, matchsticks, and pegsretained inside the perforate member;

FIG. 3 is a view of four categories of particles thrown out through theholes in the perforate members, grit, stone, sawdust, and barkparticles;

FIG. 4 is a plan view of a separator with which the invention may bepracticed;

FIG. 5 is a side elevation of said separator;

FIG. 6 is an auxiliary view at 66 of FIG. 5; and

FIG. 7 is an enlarged, partial, vertical sectional view showing theperforate member and adjacent parts.

Referring now more particularly to the drawings, there is shown in FIG.5 a separator indicated generally at 10 with a head 12 having a smoothcylindrical inner surface 14 and an inlet portion 16 and gas outlet 17.Mounted beneath surface 14 coaxially therewith is generallyfrustoconical perforate member 18, with an unperforated smooth upperportion 20 for initially accepting downwardly dropping particles withoutundue wear, and a perforate lower portion 22, which terminates inexhaust portion 24. Particles passing through the holes in perforatemember 18 are caught by frustoconical member 26 and emerge throughexhaust 28.

Conduit 30 is connected to inlet portion 16 through transition piece 32,which is round like the conduit at its conduit end 34, and rectangularlike inlet portion 16 (with three times the round end cross-sectionalarea) at its inlet portion end. Inlet portion 16 (and other portionssubject to heavy particle wear) may if desired be provided with liners.

In operation, a mixture of chips 40, pegs 42, matchsticks 44 (the lattertwo being industry expressions for bits of fibrous wood ofcharacteristic shape), grit 46, stone 48, sawdust 50, and bark 52 ispneumatically carried by air (0.2 pound of air per pound of particles inthe preferred embodiment; the range is 0.15 to 1.0) through conduit 30at 10,000 feet per minute. The crosssectional area of the conduit isabout 78 square inches and that of the inner portion 16 about 200 squareinches, so the air is slowed to a velocity of about 3,400 feet perminute in the transition piece 32. The particles, however, throughinertia keep most of their 10,000 feet speed, whereby a considerablespeed differential between air and particles is produced in thetransition piece. This speed differential makes elongated particlesswing so that their longest dimension becomes generally perpendicular tothe direction of flow. In inlet portion 16, then, the curve brings theparticles into a thinned layer away from the center of curvature.Actually, in this embodiment, conduit 30 has an inner diameter of about12 inches, while inner portion 16 has a cross-sectional inner area of 12inches by 20 inches; the layer formed is however only about an inchthick, with the largest dimension of many chips 40 about inch. Thesecombined alignment and thinning steps permit introduction of theparticles over cylindrical surface 14 generally tangentially thereto,and with a particle surface of each elongated particle corresponding tothe longest dimension thereof generally against surface 14 upon impacton surface 14. This relationship is then maintained and reinforced asthe particles spin around and around as they move downwardly oversurfaces 14, 20, and 22 (as they leave the latter the particles stillhave a speed of about 1000 feet per minute). Although the holes inperforate member 20 are inch in diameter, the material which passestherethrough looks like that passed by a conventional inch screen. Thussmall material is ejected through holes three times as large indiameter, with consequent increase in speed, elimination of blocking,and increase in efiiciency; alignment of the elongated pegs andmatchsticks makes them bridge holes they would easily be lost throughotherwise, saving them and avoiding a great loss of valuable fibrousmaterial. Furthermore, alignment prevents wedge-shaped elongatedparticles from starting into holes and then blocking them. And the highturbulence created by the particle speeds involved prevents any build-upat the holes of fibrous, gummy, or other material.

Particles with more than one dimension greater than the hole size, suchas many chips 40, are of course retained with the elongated particles,on conventional principles.

Other embodiments of the invention will be apparent to those skilled inthe art and are within the following claims.

I claim:

1. The method of separating elongated particles with a longest firstdimension from other particles all dimensions of which are less thansaid first dimension which comprises moving all said particles incontact with a gaseous medium, providing a differential velocity betweensaid particles and said medium sufficient to align said elongatedparticles with their longest dimension generally perpendicular to thedirection of their flow, thereafter guiding said particles onto an innersurface circular in cross-section, and moving said particles circularlyand downwardly over holes large enough to accept all dimensions of saidelongated particles except said first dimension.

2. The method of separating elongated particles with a longest firstdimension from other particles all dimensions of which are less thansaid first dimension which comprises moving all said particles incontact with a gaseous medium, providing a differential velocity betweensaid particles and said medium sufficient to align said elongatedparticles with their longest dimension generally perpendicular to thedirection of their flow, thereafter bringing said particles together ina thinner layer, guiding said thinner layer tangentially onto an innersurface circular in cross-section, and moving said particles circularlyand downwardly over holes large enough to accept all dimensions of saidelongated particles except said first dimension.

3. The method of claim 2 in which said elongated particles are wood pegsand matchsticks and said other particles include bark and sawdust.

4-. The method of claim 3 in which said holes are round and of diametera plurality of times greater than the largest dimension of the bulk ofsaid other particles.

5. The method of claim 2 in which said particles and said gaseous mediuminitially move together and at a speed in excess of 5000 feet perminute.

6. The method of claim 5 in which said speed is 10,000 feet per minute.

7. The method of claim 5 in which the velocity of said medium is reducedat least just before said particles are brought together in said thinnerlayer.

8. The method of claim 2 in which said thinner layer is produced bycentrifugal action on said particles.

9. The method of claim 2 in which said layer is of thickness less thantwice the largest dimension of particles ordinarily present therein.

10. The method of claim 5 in which said gaseous medium is air and theweight ratio thereof to said particles is 0.15 to 1.0.

11. The method of claim 10 in which said ratio is 0.2.

References Cited UNITED STATES PATENTS 603,285 5/1898 Porbeck 209-250 X938,702 11/1909 Porbeck 209250 X 1,224,898 5/1917 Brennen 209-1442,991,883 7/1961 Hendrickson 209-144 OTHER REFERENCES Taggart: Handbookof Mineral Dressing, 1945 (9-10 through 9l3 FRANK W. LUTTER, PrimaryExaminer.

HARRY B. THORNTON, Examiner.

R. HALPER, Assistant Examiner.

1. THE METHOD OF SEPARATING ELONGATED PARTICLES WITH A LONGEST FIRSTDIMENSION FROM OTHER PARTICLES ALL DIMENSIONS OF WHICH ARE LESS THANSAID FIRST DIMENSION WHICH COMPRISES MOVING ALL SAID PARTICLES INCONTACT WITH A GASEOUS MEDIUM, PROVIDING A DIFFERENTIAL VELOCITY BETWEENSAID PARTICLES AND SAID MEDIUM SUFFICIENT TO ALIGN SAID ELONGATEDPARTICLES WITH THEIR LONGEST DIMENSION GENERALLY PERPENDICULAR TO THEDIRECTION OF THEIR FLOW, THEREAFTER GUIDING SAID PARTICLES ONTO AN INNERSURFACE CIRCULAR IN CROSS-SECTION, AND MOVING SAID PARTICLES CIRCULARLYAND DOWNWARDLY OVER HOLES LARGE ENOUGH TO ACCEPT ALL DIMENSIONS OF SAIDELONGATED PARTICLES EXCEPT SAID FIRST DIMENSION.